<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title></title>
    <script>
        var num=1;
        function changeImg() {
            var img=document.getElementById("lbt");
            img.src="img/"+(++num==6?num=1:num)+".jpg"
        }
    </script>
</head>
<body onload="setInterval('changeImg()',1000)">
    <table>
        <tr>
            <td>
                <img src="img/1.jpg" width="100%">
            </td>
        </tr>
    </table>
</body>
</html>